Processes for the decomposition of crude phosphate



Patented June 16, 1931 UNITED STATES PATENT, OFFICE THEODOR 'rrroRssELI. AND AUGUST xnIsrENssoN, or GASSEL, GERMANY PROCESSES FOR THE DECOMPOSITION OF CRUDE PHOSPHATE No Drawing. Application filed November 11, 1929, SerialNo. 406,504, and in Germany November 28, 1928.

It is already known to use a mixture of potassium sulphate and an acid for the decomposition of crude phosphates in place of sulphuric acid. This method of working is 6 rational, since the value of the potassium sulphate lies exclusively in the potash and the sulphuric acid is therefore introduced into the process without cost. If nitric acid is used, gypsum and a solution of po- 1 tassium nitrate and phosphoric acid or a potassium vphospate or a mixture of both are obtained; it is also possible, by evaporating this solution after previous neutralization, make a which limits.

It has now been proved by experiments that owing to excessive losses of potash this process "cannot be carried out forthwith. The whole economy of the process may be ruined becaus the potash, as stated above, is the valuable constitutent of potassium sulhate.

This loss in potash arises because not only gypsum is formed in the decomposition but also, according to the concentration and the temperaturasyngenite (K SO CaSO ,H O)

mixed fertilizer, the composition of may be varied within somewhat wide or pentasulphate (K SO 502180 H 0),

60 If, or instance,

which precipitate out together with the gypsum and are lost with it (cf. Gmelin-Kraut Handbuch der Anorganischen Chemie, 7th edn., Vol. II, Part I, p. 139).

These double salts are decomposed by water (of. J. H. vant Hofi, Untersuchungen iiber die Bildungsverhaltnisse der Ozeanischen Salzablagerungen, Insbesondere des Stassfurter Salzlagers, pp. 290, 291). By washing with watertherefore the potash could be recovered from the gypsum slime, butquantities of heat are then necessary which are so large that the lye obtained is diluted to such an extent that working in this manner is practically impossible.

The invention consists in effecting the washing of the potash fromthese double com ounds in presence of some free acid. pentasulphate is treated at e. g. with ammonia or potash, to

20 C. with acidified water, improved results are obtained with 100 g. H20+2.7 g. HNOS are dissolved 5.8 g. K2804 with 100 g. H2O+6.1 g. HNO are dissolved 9.5 g K2SO4 whereas accordingto vant Hofl only 3.58 g. K 80 are dissolved in 100 g. H O at 31.8 C.

The process is carried out in such a manner that the washing of the gypsum slime containin the potassium-calcium double salts is efiected in two stages with an intermediate agitation with a dilute water solution of the particular acid being used. First of all, therefore, the gypsum sllme is washed with a part of the quantity of washing water as usual; it is then agitated. with water containing acid and is finally completely washed out with water.

The acid from the stirring lye together with the last washing water is employed, as usual, for the decomposition of fresh crude phosphate.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is l.-In a process for the decomposition of crude phosphate with an acid and potassium sulphate with precipitation of gypsum containing double potassium-calcium salts, the recovery of the potash from the said double salts, comprising the steps of washing with water the gypsum containing the said double salts, agitating with water, containing nitric acid, and washing again with water, as set forth.

2. In a process for the decomposition of crude phosphate with recovery'of the potash, as claimed in claim 1, the use of the acid washing liquor obtained in the second step of the recovery in the decomposition of fresh crude phosphate, as set forth.

In testimony tures.

THEODOR THQRSSELL. AUGUST KRISTENSSON.

whereof we afiix our signa- 

